Option C — Ireland
Ireland was the most affected by the potato famine during 1845–1849, which led to mass starvation and large-scale emigration of Irish people to America and Australia.
Source: A World Economy Takes Shape, Chapter 3
The source passage references Irish emigrants leaving for the US (Fig. 7) in the context of mass migration caused by hardship, indicating Ireland as the country most severely affected. The potato famine causing mass Irish emigration is a well-known historical fact supported by the textbook context. Examiners expect the direct, correct option — no elaboration needed for 1 mark.